Phytosterols and their derivatives hardened by hydrogenation, phytostanols, have been known for many years for their cholesterol-lowering properties. As early as 1991, researchers demonstrated the effectiveness of these substances in inhibiting the absorption of cholesterol in the intestine and through the inner blood vessel walls. Accordingly, sterols and stanols are widely used in the food industry because, through their hypocholesterolaemic effect, they minimize future diseases, such as atherosclerosis, heart disease and hypertension. Since phytosterols and stanols are insoluble in water and only poorly soluble in fats and oils, the incorporation of these cholesterol-lowering agents in food preparations, cosmetic or pharmaceutical products poses considerable problems. The unfavourable solubility behaviour of the substances results not only in poor dispersibility, but also in reduced bioavailability and in unsatisfactory stability of the food preparations.
Efforts to solve this problem have included the formulation of small particle sizes, mainly by micronization. However, the micronization of the sterol particles is not in itself sufficient to enable satisfactory incorporation into food products. Although the bioavailability of the finely dispersed particles can be improved by increasing the surface area, the micronized particles show poor wetting behaviour, readily aggregate, and generally float on the surfaces of aqueous dispersions. In many cases, the ground sterol can only be dispersed in a beverage by special methods involving intensive mixing. However, intensive mixers are not normally available to the end user of the food manufacturers.
Accordingly, many manufacturers combine micronization of the sterols with the additional use of emulsifiers.
European patent EP 0897671 B1 claims food especially beverages containing aqueous suspensions or dispersions with sterols and sterol esters having a particle size of 15 micron or lower and a non-sterol emulsifier in a weight ratio emulsifier to sterol of less than 1:2. The non-sterol emulsifier could be monoglycerides, diglycerides, polysorbates, sodium stearyl lactylate or polyglycerol esters.
In US 20040033202 A1 the applicant has claimed a composition comprising: (a) particles of at least one sterol or a salt thereof, wherein the sterol particles have an effective average particle size of less than about 2000 nm; and (b) at least one surface stabilizer. The suggested emulsifiers, especially polysorbates are claimed as surface stabilisers in this application.
International application WO 2002/065859 A1 discloses a method of dispersing phytosterol in an aqueous phase, which comprises mixing particulate phytosterol with an aqueous phase in the presence of a non-sterol emulsifier having a HLB value higher than that of the phytosterol to create an aqueous phytosterol dispersion, such that the combined HLB value of the non-sterol emulsifier and the phytosterol in the aqueous phase does not exceed 8.
U.S. Pat. No. 6,623,780 B1 claims compositions with sterols, monoglycerides and polysorbates in a defined weight ratio having a particle size smaller than one micron when dispersed in water. Compositions containing one part sterol to 1.14 to 1.5 parts monoglycerides and 0.04 to 0.2 parts polysorbate are protected as well as the process of preparing a beverage containing these ingredients.
Not only the addition of surfactants, but also manufacturing steps should improve water-dispersibility of the sterol particles.
WO2003105611 A2 claims a process for producing a plant sterol dispersion, which requires a heating step, the dispersion containing sterols which is just characterised by the particle size distribution from 0.1 to 30 μm.
A method of forming a plant sterol-emulsifier dispersion for use in a food product, including micromilling at, or close to, or below ambient temperature to form the plant sterol-emulsifier dispersion, wherein the average particle size of the plant sterol-emulsifier dispersion is about 1 to about 40 microns is claimed in the European application EP 1142494 A1. In addition it claims the plant sterol-emulsifier dispersion with having an average particle size of about 1 to about 40 microns.
The particle size of the micronised sterol particles should be as small as possible in order to have a large surface area, so that availability of the sterol could be improved.
Often the addition of a surfactant is sufficient to achieve a better water-dispersibility of the micronised sterol particles, but further processing of the dispersion and incorporation in food formulations is unsatisfactory as the nature of the chosen surfactant greatly influences the characteristics of the sterol particle containing dispersion.
The problem addressed by the present invention was to provide a formulation which would allow the effective dispersion and incorporation of sterols, stanols and esters thereof in foods especially beverages while using simple equipment. The sterol formulation would be readily produced and would be distinguished by high stability in storage.